As a method for allowing a viewer to view stereoscopic images without using special glasses, the parallax barrier method and the lenticular lens method have been known since before. For example, JP2004-264760A (Patent Document 1) discloses a stereoscopic video display device that includes a switching liquid crystal panel that is capable of realizing a parallax barrier in which openings for transmitting light and light-shielding parts for blocking light are arrayed alternately. In the parallax barrier method, however, though it is possible to switch 2D display and 3D display from one to the other without a decrease in the resolution during 2D display, brightness during 3D display is 50% or less as compared with that during 2D display, due to the left-right image separation necessary for stereoscopic display, which is achieved by blocking light with light-shielding parts.
On the other hand, in the lenticular lens method, since a lens sheet is attached over a display panel so that images are separated by the light condensing effect of the lenses, the brightness during 3D display at the same level or higher as compared with that during 2D display can be ensured. During 2D display, however, the resolution in the horizontal direction becomes 1/2 or less (the resolution becomes 1/N if the number of viewing points is N), since the light condensing effect is exhibited during 2D display as well.
In this way, both of the parallax barrier method and the lenticular lens method have advantages and disadvantages. As a method that attempts to improve these disadvantages, the liquid crystal lens method is available. For example, JP2004-258631A (Patent Document 2) and JP2009-520231T (Patent Document 3) disclose a stereoscopic display device in which a voltage is applied across a pair of substrates so that pseudo lenses are formed in a liquid crystal layer sealed between these substrates in pair. In the stereoscopic display device disclosed in Patent Documents 2 and 3, however, a desired lens effect could hardly be exhibited at boundary areas between adjacent two of the lenses, which causes the crosstalk ratio to deteriorate. Besides, since the image separation is performed only by light condensing by the liquid crystal lenses, it is necessary that the liquid crystal layer has to have a greater thickness in order to achieve a satisfactory light condensing effect, which causes a problem that the switching speed for the switching between 2D display and 3D display decreases. In addition to this, it is significantly difficult to keep the cell thickness uniform, which causes a problem of poor mass producibility.